The bias is obvious. For example, if a person is badly done in some way and has an association with Trump and Clinton, then only the link to Trump is mentioned.
The same goes for people who have ties to Russia and who also work for the FBI. If they can be used to defame Trump, only his link to Russia is mentioned.
Mueller uses media articles to back up his claims, not to mention that the article happened because they leaked the details to the media.
There is a lot to criticize.